/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
namespace tf_backend {
  export type Listener = () => void;

  // A unique reference to a listener for an easier dereferencing.
  export class ListenKey {
    public readonly listener: Listener;
    constructor(listener: Listener) {
      this.listener = listener;
    }
  }

  export abstract class BaseStore {
    protected requestManager: RequestManager = new RequestManager(
      1 /* simultaneous request */
    );
    private _listeners: Set<ListenKey> = new Set<ListenKey>();
    public initialized: boolean = false;

    /**
     * Asynchronously load or reload the runs data. Listeners will be
     * invoked if this causes the runs data to change.
     *
     * @see addListener
     * @return {Promise<void>} a promise that resolves when new data have loaded.
     */
    protected abstract load(): Promise<void>;

    refresh(): Promise<void> {
      return this.load().then(() => {
        this.initialized = true;
      });
    }

    /**
     * Register a listener (nullary function) to be called when new runs are
     * available.
     */
    addListener(listener: Listener): ListenKey {
      const key = new ListenKey(listener);
      this._listeners.add(key);
      return key;
    }

    /**
     * Remove a listener registered with `addListener`.
     */
    removeListenerByKey(listenKey: ListenKey): void {
      this._listeners.delete(listenKey);
    }

    protected emitChange(): void {
      this._listeners.forEach((listenKey) => {
        try {
          listenKey.listener();
        } catch (e) {
          // ignore exceptions on the listener side.
        }
      });
    }
  }
} // namespace tf_backend
